1. Field of the Invention
The present invention relates to a link establishing system and a link establishing method for confirming whether bi-directional data transmission is enabled through a pair of optical transmission devices connected to each other between a first device and a second device.
2. Description of the Related Art
As a technology associated with this type of link establishing system, there is a synchronizing system or the like disclosed in, e.g., Japanese Patent Application Publication No. Sho 63-9705 and "DRAFT PROPOSED INTERNATIONAL STANDARD--Fiber channel--Physical and Signalling Interface", pp. 71-89, issued by ISO. As shown in FIG. 3, such a synchronizing system is constituted by a pair of optical transmission devices 33 and 34 connected with each other through an optical fiber 41 between an upper device 31 and a lower device 32, and judgment is made upon whether the bi-directional data transmission is possible between the upper device 31 and the lower device 32 by executing a process called "handshake" through the optical transmission devices 33 and 34.
In this synchronizing system, in order to execute the handshake process, a specific pattern is first generated by a specific pattern generating circuit 42 of the optical transmission device 33 in the upper device 31, and the specific pattern is converted into an optical signal using an electric signal/optical signal converting circuit 36, the converted optical signal being transmitted to the optical transmission device 34 in the lower device 32 via the optical fiber 41 in accordance with the timing of a clock signal fed from a clock generating circuit 40.
In the optical transmission device 34, the optical signal supplied from the upper device 31 is received by an optical signal/electric signal converting circuit 38, and the optical signal is thereby converted into an electric signal as a receive signal. The receive signal is input to a specific pattern detecting circuit 43 that makes judgment upon whether a specific pattern is included in the receive signal and outputs a receive data signal indicating the result of the judgment. Although the receive data signal is input to a response circuit 44, the receive data signal is transmitted to the electric signal/optical signal converting circuit 36 if the receive data signal indicates that the specific pattern has been detected. The electric signal/optical signal converting circuit 36 converts the receive data signal into an optical signal, the optical signal being returned to the upper device 31 over the optical fiber 41 in accordance with a timing of the clock signal from the clock generating circuit 40.
In the optical transmission device 33 in the upper device, the optical signal fed from the lower device 32 is subsequently received in the optical signal/electric signal converting device 38 and converted into an electric signal as a receive signal. The receive signal is input to a specific pattern detecting circuit 43 that detects if a specific pattern is included in the receive signal or not.
If the specific pattern is detected in the specific pattern detecting circuit 43, it is possible to confirm the following states. That is, the optical transmission device 33 in the upper device 31 can appropriately perform transmission; the specific pattern fed from the upper device 31 can be appropriately received by the optical transmission device 34 in the lower device 32; the optical transmission device 34 can adequately effect transmission; and the optical transmission device 33 in the upper device 31 can adequately carry out reception. It has been therefore confirmed that the bi-directional data transmission is possible between the upper device 31 and the lower device 32, thereby establishing the link.
It is to be noted that a transmitting circuit 37, a receiving circuit 35 and a synchronizing signal extracting circuit 39 in each of the optical transmission devices 33 and 34 function when actually transmitting data between the upper device 31 and the lower device 32 in the bi-directional manner after establishing the link.
In case of the above-mentioned synchronizing system (link establishing system), the specific pattern generating circuit is provided to the optical transmission device in the upper device and the handshake for sending/receiving the specific pattern between the upper device and the lower device is effected to establish the link, which makes the processing procedure to establish the link troublesome, thus enlarging and complicating the circuit configuration required in the optical transmission device.
Further, there is a difference between the upper device and the lower device in provision of the specific pattern generating circuit in the optical transmission device configuration, and hence sharing of data transmission between the upper device and the lower device is not smoothly ensured, resulting in troublesome and inconvenient design development or maintenance of the optical transmission device.